Propylene glycol ether is one of the important industrial derivatives of epoxy compounds which mainly produced by the reaction of propylene oxide and an alcohol. Propylene glycol ether has alcohol ether group and hydroxyl group with strong dissolving function, such that it has very strong dissolving property and is known as a universal solvent which is widely used in coating, ink, paint, and printing, etc. Due to steric hindrance effect, the ring-opening position of propylene oxide is different under acidic or alkali condition, so that the addition reaction between the resultant therefrom and an alcohol gives different product, with 1-methoxy-2-propanol being generated under the alkali condition, and 2-methoxy-1-propanol being generated under the acidic condition.

So far, during acidic catalysis, selectivity for resultant is not high, and the ratio of I and II mainly depends on acid strength. Moreover, as the toxicity of product I is higher than that of product II, there has been increasing interest in alkali catalytic synthesis of propylene glycol ether. However, the product of alkali catalysis is predominantly 1-methoxy-2-propanol. According to traditional mechanism, an alkali catalysis reaction is conducted by deprotonation of alcohol under the action of alkali to obtain alkoxy ion, thereafter the alkoxy ion promote the ring-opening of propylene oxide to render an addition reaction. Homogeneous alkali catalyst can be selected from a group consisting of NaOH, NaOR(NaOCH3), NR3 organic amine or NH3, however, all of them have disadvantages such as equipment corrosion and being difficult to recycle.
An ionic liquid generally refers to an organic salt having a melting point below 100° C. It is composed of anion and cation and can have very unique physical and chemical properties by changing the anion and cation, thus it earns more and more attentions. So far, the ionic liquid has been widely used in fields such as electrochemistry, catalysis, and extraction. In the field of catalysis, it is often thought that the ionic liquid as a catalyst can change the reaction pathway. A tetramethylguanidine-based ionic liquid synthesized by Han et al. has higher reactivity and selectivity for the reaction between propylene oxide and an alcohol; however, such kind of ionic liquid is very expensive, limiting its large-scale industrial application.